TY - JOUR
T1 - Two-stage partial melting and contrasting cooling history within the Higher Himalayan Crystalline Sequence in the far-eastern Nepal Himalaya
AU - Imayama, Takeshi
AU - Takeshita, Toru
AU - Yi, Keewook
AU - Cho, Deung Lyong
AU - Kitajima, Kouki
AU - Tsutsumi, Yukiyasu
AU - Kayama, Masahiro
AU - Nishido, Hirotsugu
AU - Okumura, Tasuku
AU - Yagi, Koshi
AU - Itaya, Tetsumaru
AU - Sano, Yuji
N1 - Funding Information:
We wish to thank K. Suzuki, T. Kato and their colleagues (Nagoya University) for useful discussion on this study. We also greatly thank T. Danhara and H. Iwano (Kyoto Fission Track Corporation) for fission track zircon analyses and H. G. Kim (Korea Basic Science Institute) for U–Pb zircon analyses using the SHRIMP instrument. We appreciate the reviews by three anonymous reviewers, which have greatly improved the quality of manuscript. The authors also thank M. Scambelluri for editorial handling of the manuscript and correction of the English text. This research was supported by grant from Leave a Nest Co., Ltd. and Discover 21, Inc . This study was also supported in part by grants from Center for Chronological Research, Nagoya University, Kazato Research Foundation and JSPS Fellows to K. Kitajima (No. 19-6362 ).
PY - 2012/3
Y1 - 2012/3
N2 - The timing of partial melting and the pressure-temperature (P-T) paths in the High Himalayan Crystalline Sequence (HHCS) in far-eastern Nepal has been investigated using zircon chronology, rare earth element (REE) compositions, and P-T pseudosection analysis. Zircon from migmatites formed during Himalayan thermal events displays inherited magmatic core overgrown by two generations of metamorphic rims. The new rims are distinguished on the basis of their Tertiary ages, low MREE contents, and low Th/U ratios. The inner zircon rims from Sil. +. Grt. +. Bt. +. Kfs. +. Pl. +. Qtz and Ky. +. Sil. +. Grt. +. Bt. +. Ms. +. Pl. +. Qtz migmatites at different structural level of the HHCS display ages of c. 33-28. Ma (Early Oligocene) and c. 21-18. Ma (Early Miocene): these rims are characterized by flat MREE to HREE patterns and were overgrown by partial melt through muscovite dehydration melting under the stability of garnet, which occurred at P=c. 7-10. kbar and T=c. 730-780°C, and at P=c 8-14. kbar and T=c 720-770°C, respectively. The outer zircon rims are relatively enriched in HREE with respect to the inner rims and were overgrown at c. 27-23. Ma (Late Oligocene) and at c. 18-16. Ma (Early Miocene) during melt crystallization accompanying breakdown of garnet at P=. c. 4-7. kbar and T=. c. 650-725°C. Early Miocene Ms-Bt leucogranites with two successively overgrown zircon rims at c. 18.3±0.3. Ma and c. 16.3±0.2. Ma were intruded into Early Oligocene migmatite hosts. Microstructural observations and the corresponding P-T conditions associated with the two generations of zircon rims indicate that the Early Oligocene and Early Miocene migmatites show relatively isobaric and nearly isothermal P-T paths during exhumation, respectively. The inferences are consistent with higher average cooling rates for the Early Miocene (c. 30-40 °C/My) than the Early Oligocene (c. 15-25. °C/My) migmatites, inferred from peak-. T conditions and FT (c. 6. Ma for both migmatites) and U-Pb zircon ages. The P-T-t paths of the two migmatites indicate that burial of the Early Miocene migmatites has been coeval with exhumation of the Early Oligocene migmatites, implying the formation of large-scale thrust within the HHCS.
AB - The timing of partial melting and the pressure-temperature (P-T) paths in the High Himalayan Crystalline Sequence (HHCS) in far-eastern Nepal has been investigated using zircon chronology, rare earth element (REE) compositions, and P-T pseudosection analysis. Zircon from migmatites formed during Himalayan thermal events displays inherited magmatic core overgrown by two generations of metamorphic rims. The new rims are distinguished on the basis of their Tertiary ages, low MREE contents, and low Th/U ratios. The inner zircon rims from Sil. +. Grt. +. Bt. +. Kfs. +. Pl. +. Qtz and Ky. +. Sil. +. Grt. +. Bt. +. Ms. +. Pl. +. Qtz migmatites at different structural level of the HHCS display ages of c. 33-28. Ma (Early Oligocene) and c. 21-18. Ma (Early Miocene): these rims are characterized by flat MREE to HREE patterns and were overgrown by partial melt through muscovite dehydration melting under the stability of garnet, which occurred at P=c. 7-10. kbar and T=c. 730-780°C, and at P=c 8-14. kbar and T=c 720-770°C, respectively. The outer zircon rims are relatively enriched in HREE with respect to the inner rims and were overgrown at c. 27-23. Ma (Late Oligocene) and at c. 18-16. Ma (Early Miocene) during melt crystallization accompanying breakdown of garnet at P=. c. 4-7. kbar and T=. c. 650-725°C. Early Miocene Ms-Bt leucogranites with two successively overgrown zircon rims at c. 18.3±0.3. Ma and c. 16.3±0.2. Ma were intruded into Early Oligocene migmatite hosts. Microstructural observations and the corresponding P-T conditions associated with the two generations of zircon rims indicate that the Early Oligocene and Early Miocene migmatites show relatively isobaric and nearly isothermal P-T paths during exhumation, respectively. The inferences are consistent with higher average cooling rates for the Early Miocene (c. 30-40 °C/My) than the Early Oligocene (c. 15-25. °C/My) migmatites, inferred from peak-. T conditions and FT (c. 6. Ma for both migmatites) and U-Pb zircon ages. The P-T-t paths of the two migmatites indicate that burial of the Early Miocene migmatites has been coeval with exhumation of the Early Oligocene migmatites, implying the formation of large-scale thrust within the HHCS.
KW - Large-scale thrust within the HHCS
KW - Nepal himalaya
KW - P-t-t path
KW - Partial melting
KW - Zircon geochronology
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U2 - 10.1016/j.lithos.2011.12.004
DO - 10.1016/j.lithos.2011.12.004
M3 - Article
AN - SCOPUS:84855511284
VL - 134-135
SP - 1
EP - 22
JO - Lithos
JF - Lithos
SN - 0024-4937
ER -